How do you earth planes in flight?
GarageYears,
Your 'Breakers & Ground Wires' is very interesting reading, esp:
So, to the tiny meter voltage and current it exhibits < 1 Ohm but rather more resistance to the phase line?
Your 'Breakers & Ground Wires' is very interesting reading, esp:
Grounding to a Water Pipe
A bare 12 gauge copper wire was inserted into the hot wire side and the voltage was confirmed by meter to be 120 volts. It was touched directly to a cold water pipe and did not trip the breaker! This is a copper pipe and extends without interruption directly out into the earth.
The DC resistance from both the ground and neutral electrical terminals to that copper pipe was measured and found to be essentially zero. The digital ohmmeter measured about 1 ohm or less to the pipe. If the earth were acting as a simple ohmic conductor back to the ground at the service box, it would have conducted 120 amperes and would have immediately tripped the breaker.
A bare 12 gauge copper wire was inserted into the hot wire side and the voltage was confirmed by meter to be 120 volts. It was touched directly to a cold water pipe and did not trip the breaker! This is a copper pipe and extends without interruption directly out into the earth.
The DC resistance from both the ground and neutral electrical terminals to that copper pipe was measured and found to be essentially zero. The digital ohmmeter measured about 1 ohm or less to the pipe. If the earth were acting as a simple ohmic conductor back to the ground at the service box, it would have conducted 120 amperes and would have immediately tripped the breaker.
Westlakes definitely know what he is talking about
he's an electrickerical injunir
Edit; did you know that delta/wye connected transformers are being phased out
he's an electrickerical injunir
Edit; did you know that delta/wye connected transformers are being phased out
So, to the tiny meter voltage and current it exhibits < 1 Ohm but rather more resistance to the phase line?
- GY
Aircraft tyres tend to be conductive to ensure any static potential is discharged on touchdown. An old British type I used to fly actually had a copper mesh moulded into the nosewheels and you could see bit's of copper glinting in the sunlight sometimes. These days they put something in the rubber which makes the earth.
Helicopters can generate massive static potentials. If you're in the unfortunate position of having to be winched in a rescue, you may notice the winchman has an earthing lead danging from his harness. He will touch that on the surface before touching either the sea/ground or you. It's very important to let that happen - otherwise there may be a big flash and a yelp! If you're in water, it's you who will take the shock so don't be too enthusiastic to be rescued! With other rescue systems where they use either a strop or a basket, the crew will dip it in the water before it comes near you.
Helicopters can generate massive static potentials. If you're in the unfortunate position of having to be winched in a rescue, you may notice the winchman has an earthing lead danging from his harness. He will touch that on the surface before touching either the sea/ground or you. It's very important to let that happen - otherwise there may be a big flash and a yelp! If you're in water, it's you who will take the shock so don't be too enthusiastic to be rescued! With other rescue systems where they use either a strop or a basket, the crew will dip it in the water before it comes near you.
I know this is a bit of thread drift but:
If 'Earth' was strapped to Neutral, say, just before the domestic meter, would a Neutral short to Earth still trip the RCCB? i.e. like Mig15's system.
Don't worry, I have no intention of carrying out above modification
If 'Earth' was strapped to Neutral, say, just before the domestic meter, would a Neutral short to Earth still trip the RCCB? i.e. like Mig15's system.
Don't worry, I have no intention of carrying out above modification
If you're in the unfortunate position of having to be winched in a rescue, you may notice the winchman has an earthing lead danging from his harness. He will touch that on the surface before touching either the sea/ground or you.
YouTube - High Voltage Cable Inspection
If 'Earth' was strapped to Neutral, say, just before the domestic meter, would a Neutral short to Earth still trip the RCCB? i.e. like Mig15's system.
Typically the trip current imbalance will be 5mA, so any mismatch greater than this will pop the breaker. For humans as little as 50mA @ 120V can be fatal, depending exactly where the current path flows. The worst possible path is across the chest for obvious reasons, so grabbing the live and neutral lines with left and right hands is a VERY bad idea. Many electricians I know will purposefully slip their left hand into their back pocket or belt strap to ensure they don't complete a chest path if they are forced to work on a live circuit.... not something recommended ever but occasionally unavoidable.
- GY
Last edited by GarageYears; 18th May 2010 at 13:12. Reason: Incomplete sentences don't help
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who, alot of complicated ideas flying about here, so i thought i would just simplify things;
a conventional earth is not a stick into the ground, consider it a 0v reference point with a very low impedance (IE lower impedance than through your body) therefore an attractive route to compete a circuit for any stray current (IE from a loose wire or whatever) if it were to touch a metal case, and somone was in contact with that case- should the case be earthed the current would go through the earth line (AC AND DC ALIKE) instead of through you.
In an AC it is for exactly the same reason, remembering that for a current to flow there has to be a potential difference (if you and the aircraft are all at 10,000v and you touch a 10,000v wire it doesn't matter because there is no difference - hence how birds sit on power lines). Therefore an ACs earth can merely be a mass connection of everything metal that stops a difference from forming between different parts - IE connection to the neutral of the battery too. A loose wire would therefore short through the low impedance mass of metal and not through the higher impedance human flesh. On the ground, the AC ground can be connected to the real world ground so there is no difference between the AC and the rest of the world - remembering it is a difference that causes a current. you do not want this difference to equalize through the fuel hose - a grounding reel is much more preferable.
source: electronic engineering degree
a conventional earth is not a stick into the ground, consider it a 0v reference point with a very low impedance (IE lower impedance than through your body) therefore an attractive route to compete a circuit for any stray current (IE from a loose wire or whatever) if it were to touch a metal case, and somone was in contact with that case- should the case be earthed the current would go through the earth line (AC AND DC ALIKE) instead of through you.
In an AC it is for exactly the same reason, remembering that for a current to flow there has to be a potential difference (if you and the aircraft are all at 10,000v and you touch a 10,000v wire it doesn't matter because there is no difference - hence how birds sit on power lines). Therefore an ACs earth can merely be a mass connection of everything metal that stops a difference from forming between different parts - IE connection to the neutral of the battery too. A loose wire would therefore short through the low impedance mass of metal and not through the higher impedance human flesh. On the ground, the AC ground can be connected to the real world ground so there is no difference between the AC and the rest of the world - remembering it is a difference that causes a current. you do not want this difference to equalize through the fuel hose - a grounding reel is much more preferable.
source: electronic engineering degree
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Many electricians I know will purposefully slip their left hand into their back pocket or belt strap to ensure they don't complete a chest path if they are forced to work on a live circuit
